Water lines often have the possibility of freezing, particularly water lines onboard passenger transportation vehicles that experience extreme temperature changes. For example, water lines on board aircraft have the possibility of freezing during flight or on normal ground use in certain environments. If water freezes in a water line, this can cause pipe rupture, disruption of normal water flow, damage to end structures, as well as a number of other problems. It is thus desirable to protect water lines against freezing.
Some solutions have been to provide spot heating on water lines in order to prevent them from freezing. One attempted solution has been to provide an external jacket around the water lines in order to keep them at a desired temperature that is lower than the freezing point. Other solutions have been to use an inline water heater that is routed inside the water line 10. Examples of this solution are shown in FIGS. 1 and 2.
The heater element may be resistance heating wire 12 that is sealed inside a tube 14 (e.g., in some instances, a Teflon tube). The wire 12 and a tube 14 combination is then inserted inside the water line 10. The water system plumbing may have various lengths of in-line water heaters positioned in the water lines at various locations along the water system plumbing. These inline water heaters are operated by a controller 16 that monitors the temperature of the heater, which is determined by one or more temperature sensors 18. The controller 16 is installed hardware that can control the heater element in order to avoid continuous operation of the heater. This is generally intended to maximize efficiency of the system so that they are not constantly heating, but instead, only heat when needed. The in-line heaters are not provided to heat the water in the water lines; they are provided to prevent freezing of the water in the water lines, so need only heat the water to a point above freezing. Accordingly, in-line heating may not be required in a warm environment and/or on a hot day.
In use, when the controller 16 senses that the set point at which the heater element should turn on has been reached (i.e., the temperature is approaching freezing), the controller 16 activates the heater wires/elements. When the controller 16 senses that the set point at which the heater element should turn off has been reached (i.e., the temperature is at a safe level where freezing will not occur), it turns off the heater wires/elements. The controller 16 switches the in-line heaters on and off by commanding corresponding circuit breakers that power the heater wires/elements 12 on and off. The controller 16 communicates with the one or more temperature sensors 18 in order to make this determination.
The temperature sensors 18 may be internal to the inline heater system or external to the heater system. FIG. 1 illustrates an in-line heater with an external temperature sensor. FIG. 2 illustrates an in-line water heater with an internal temperature sensor.